Rotary hearth furnace and system for forming balls

ABSTRACT

A rotary hearth furnace comprising a single, unitary heating chamber the rotatable hearth of which is provided with a plurality of openings to receive turntables which are also rotatable, each turntable having a spindle to receive a coil or coils of rod. The furnace is provided with a charging station having a lift mechanism which is movable from a retracted position beneath the hearth into engagement with a properly positioned turntable so as to enable the turntable to be raised out of contact with the hearth framework so that a coil may be deposited on the turntable about the spindle without putting undue strain on the hearth framework. The lift mechanism is capable of raising the turntable high enough above the hearth so that, when desired, the mechanism which is used normally to charge the coil of rod onto the turntable may be used to remove the turntable from the furnace. The furnace is also provided with an unreeling station having both a lift mechanism and a turntable rotating mechanism, all of which is movable from a retracted position beneath the hearth to an elevated position so as to move a turntable from contact with the hearth framework so that the rotating mechanism may be actuated to rotate that turntable in either direction as desired. This lift mechanism may raise this turntable to a more elevated position to enable any debris collecting between the turntable and the hearth to be cleared. An indexing mechanism is provided which moves the hearth and its turntables in a step by step fashion. A coil conveyor is provided by means of which a succession of coils of rod is brought to the charger which then places the coils in the furnace on a turntable at the charging station. The heated rod leaves the furnace from the unreeling station and is adapted to be fed immediately to a ball forging apparatus, whereafter such balls are immediately fed to a pancake sizer whereby the balls are finished to a truly spherical shape. After a coil is unreeled into the forging apparatus, the rotary hearth is indexed so as to bring the next turntable into such a position that a coil of rod thereon may also immediately be fed into such forging apparatus; this is continued so long as the forging apparatus is to be fed with rod, additional coils of rod being charged into the furnace on the emptied turntables as they are brought into charging position. Heating of a coil takes place as it moves through the furnace from charging position to unreeling position. Preferably the furnace is gas fired through burners located about the ceiling thereof.

United States Patent [191 Lowderrnan et a1.

[11] 3,827,267 [451 Aug. 6, 1974 1 ROTARY HEARTH FURNACE AND SYSTEM FER FORMHNG BALLS [75] Inventors: Ernest W. Lowderman,

Independence, Mo; Leland L. Harrington, Overland Park, Kans; Ferdinand Young, Jr., Independence, Mo.

[73] Assignee: Armco Steel Corporation,

Middletown, Ohio 22 Filed: 0et.16,l972 21 App1.No.: 297,886

[52] US. Cl 72/69, 72/128, 432/122, 432/124 [51] Int. Cl B2111) 27/06 [58] Field of Search 72/69, 128; 266/2 R, 2 A, 266/5 F; 432/122, 124, 78.6, 79,80, 81, 8,

Primary ExaminerCharles W. Lanham Assistant Examiner-.lames R. Duzan 1 Attorney, Agent, or Firm-John W. Melville; Albert E. Strasser; Stanley H. Foster [57] ABSTRACT A rotary hearth furnace comprising a single, unitary heating chamber the rotatable hearth of which is provided with a plurality of openings to receive turntables which are also rotatable, each turntable having a spindle to receive a coil or coils of rod. The furnace is pro vided with a charging station having a lift mechanism which is movable from a retracted position beneath the hearth into engagement with; a properly positioned turntable so as to enable the turntable to be raised out of contact with the hearth framework so that a coil may be deposited on the turntable about the spindle without putting undue strain on the hearth framework. The lift mechanism is capable of raising the turntable high enough above the hearth so that, when desired, the mechanism which is used normally to charge the coil of rod onto the turntable may be used to remove the turntable from the furnace. The furnace is also provided with an unreeling station having both a lift mechanism and a turntable rotating mechanism, all of which is movable from a retracted position beneath the hearth to an elevated position so as to move a turntable from contact with the hearth framework so that the rotating mechanism may be actuated to rotate that turntable in either direction as desired. This lift mechanism may raise this turntable to a more elevated position to enable any debris collecting between the turntable and the hearth to be cleared. An indexing mechanism is provided which moves the hearth and its turntables in a step by step fashion. A coil conveyor is provided by means of which a succession of coils of rod is brought to the charger which then places the coils in the furnace on a turntable at the charging station. The heated rod leaves the furnace from the unreeling station and is adapted to be fed immediately to a ball forging apparatus, whereafter such balls are immediately fed to a pancake sizer whereby the balls are finished to a truly spherical shape. After a coil is unreeled into the forging apparatus, the rotary hearth is indexed so as to bring the next turntable into such a position that a coil of rod thereon may also immediately be fed into such forging apparatus; this is continued so long as the forging apparatus is to be fed with rod, additional coils of rod being charged into the furnace on the emptied turntables as they are brought into charging position. Heating ofa coil takes place as it moves through the furnace from charging position to unreeling position. Preferably the furnace is gas fired through burners located about the ceiling thereof.

3 Claims, 12 Drawing Figures PATENTED NIB 6 1974 SNEEI '1 UP 8 PATENTED RUB 51974 SHEU 5 0f 8 PAIENIEMIB 61914 3.827. 267

SHEET 7 {IF 8 ROTARY HEARTH FURNACE AND SYSTEM FOR FORMING BALLS BACKGROUND OF THE INVENTION 1. Field of the Invention The furnace of this invention, although capable of many uses, has particular utility when used as a part of the system for feeding hot rod in a substantially continuous manner to forging apparatus for forging steel balls for use in grinding mills. A typical forging apparatus is shown in U.S. Pat. Nos. 3,239,912 and 3,478,556 to Baumgartner et al. The balls coming from such forging apparatus are then shaped into a substantially true sphere by a pancake sizer such as is shown in US. Pat. No. 3,621,692 to Weed.

The forging apparatus above noted is too fast to feed with hot bars if full and proper utilization of the apparatus is to be realized. it was determined, therefore, that best utilization of the forging apparatus could be achieved if hot coils could be used for feeding the apparatus. The rotary hearth furnace of this invention provides the means by which a succession of coils of rod may be properly heated and then fed almost continuously into the forging apparatus.

2. Description of the Prior Art Although a search of the prior art was conducted in an effort to locate those United States patents most pertinent to the development at hand, no assertion is made that the best such art was located, this, however, being the intent of the search; such search developed the following US. Pat. Nos. 310,402 Fox, 734,114 Beker, 1,903,909 Cope, 2,413,228 Hepburn, 2,401,930 Hansen, 201,582 Wilmsmann, 373,463 Lenox, 444,551 Daniels, and 1,1 18,869 Kugel.

Fox discloses a rotary annealing cylinder with a plurality of rotatable annealing boxes thereon. Baker discloses a furnace having a plurality of individual, separately heated heating chambers, each chamber having a single rotatable support for a coil of rod. Cope discloses a rotary hearth with a plurality of containers for holding material to be treated, each container, however, being non-rotatable. Hepburn discloses a furnace the lower half of which, carrying fixed retorts, rotates. Hansen discloses step by step rotation of a carrier having a plurality of rotating heads thereon. The remaining patents developed by the search do not seem to be of particular significance.

SUMMARY OF THE INVENTION The furnace of this invention is a part of a system which enables optimum use of the forging and sizing apparatus above identified so that a succession of steel balls may be formed almost continuously from coiled rod of suitable material. The furnace comprises a single, unitary heating compartment completely lined with refractory material. The refractory material comprising the furnace hearth is supported by suitable framework. A plurality of evenly spaced openings are provided in the hearth and each such opening is provided with a turntable which rests within the opening, out of contact with the hearth but supported on portions of that framework which also supports the hearth. Each such turntable is provided with a spindle about which one or more coils of rod may be deposited.

Operation may begin with a first turntable being located in charging position, the furnace door being opened and a coil of rod being deposited on the so located turntable by the charger which is in turn fed by a suitable coil conveyor. The hearth is indexed so that the first turntable so charged is eventually brought to the unreeling station. In the meantime, other coils of rod are placed on the various turntables when positioned before the charger. The timing will be such that by the time the first coil travels from the charging station to the unreeling station, it will be hot enough to be fed into the forging apparatus. Each succeeding coil will also be sufficiently heated by the time it is fed into such forging apparatus, the hearth having been indexed the required number of times to bring such succeeding coil into position for unreeling into the forging apparatus.

The grinding ball sizer is in line with the forging apparatus to finish the shaping of the balls. The rotary hearth is continually indexed and the operation proceeds as stated above. New coils are loaded on an empty turntable at the loading or charging station while a feeding or unreeling operation is taking place.

The turntable positions at the charging-loading and feeding-unreeling stations have power means which rise to engage the turntables. At the charging station there is two position lifting, the first position being to stabilize the turntable and remove it from contact with the hearth frame structure while the coil of rod is deposited on such turntable, and the second position is to lift the turntable even higher so that the one piece spindle-turntable can be replaced when necessary. At the unreeling station, the power means lifts to engage the turntable then in position and to effect a rotating action to feed the coil to the operator who then feeds the coil into the forging apparatus. The power to rotate the turntable is disengaged once the coil is fed into the forging apparatus as this latter apparatus will then pull the coil itself. The turntable power means can act as a slight drag on the coil to create a small amount of desired back tension. The power means may also be actuated to lift the turntable to a high-er position to enable debris to be cleaned from between such table and the hearth proper.

The furnace is gas fired by a plurality of jets evenly disposed about the ceiling of the furnace. The furnace chamber is evenly heated to desired temperature by these jets and there are no internal partitions separating the turntables and the coils of rod located thereon one from another. The gas fired furnace normally operates slightly above atmospheric pressure.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic plan view of the rotary hearth furnace and system for forming balls from coils of suitable rod material.

FIG. 2 is a cutaway perspective view of the rotary hearth furnace of this invention FIG. 3 is a sectional view taken along the line 3-3 of FIG. 1.

FIG. 4 is a diagrammatic plan view indicating the position of the furnace hearth supports and of the indexing mechanism.

FIG. 5 is an enlarged elevational view, partly in section and partly broken away, taken on the line 5-5 of FIG. 4.

FIGS. 6, 7 and 8 are elevational views of the power means which engages the turntable when positioned at the unreeling station.

FIGS. 9, l and 11 are elevational views of the power means for engaging a turntable when positioned at the charging station.

FIG. 12 is an enlarged sectional view taken on the line 12-42 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1, the rotary hearth furnace and system for forming balls is generally illustrated. The rotary hearth furnace is indicated at 20, the coil loader at 21, the coil conveyor at 22, the forging apparatus at 23, the grinding ball sizer at 24 and the mechanical and gravity conveyors for removing the finished balls to storage and the like at 25a and 25b. The forging apparatus may be like that shown in the Baumgartner et al. U.S. Pat. Nos. 3,239,912 and 3,478,556 and, therefore, will not be described in greater detail here. Similarly, the grinding ball sizer 24 may be like that shown in the U.S. Pat. No. to Weed 3,621,692 and further description will not be set forth herein. A turntable 26a and a ball conveyor 26b transfer the forged balls from the forging apparatus 23 to the finishing sizer 24. The coil conveyor 22 delivers coils of cold rod to the charger 27 which periodically deposits one or more coils of rod on a turntable positioned at the charging station. For purposes of illustration the center of the charging station is indicated at 28 and the center of the unreeling station at 29.

In FIG. 1 the rotary hearth furnace is seen in top plan with the plumbing removed. Ten turntables 30 having spindles 31 are uniformly disposed about the furnace hearth. No coil of rod has yet been placed on the turntable 30 which is at the charging station 28. A coil of rod 32 is on that turntable 30 which is located at the unreeling station 29. Normally there will be no coil of rod on the single turntable located between the unreeling station 29 and charging station 28, noting that rotation of the hearth is in a counterclockwise direction as viewed in this FIG. 1. The remaining seven turntables 30 are all shown as having a coil or rod 32 mounted thereon.

The pairs of openings 33a and 33b schematically represent the gas fired jets by which the interior of the furnace is heated, these jets being located in the ceiling of the furnace, discharging thereinto, and being suitably fed with conventional gases through conventional plumbing (not shown) as will be understood by those skilled in the art. Although a pair of such burners 33a and 33b may be positioned for each of the turntables, it may be desirable to omit one or more of these at that position wherein the turntable is normally empty, that being the position to which the hearth is indexed immediately after a coil rod has been unreeled from the station 29 and fed into the forging apparatus 23.

Coils of rod of suitable material are placed on the coil loader 21 and thereby transferred to the coil conveyor 22. This conveyor is designed to lift the coil, actually a succession of coils, and move it to the charger 27, thereafter lowering to thereby deposit the coil on such charger. The charger is designed to move into the charging station 28 and deposit the coil on that turntable 30 then positioned there, about the spindle 31. The

furnace door 34 is located at this charging station and will, of course, be raised before the coil is charged into the furnace. After the charger 27 retracts, the door 34 will be closed, and the indexing mechanism will bring the next turntable into position, the hearth being moved in a counterclockwise direction, as viewed in FIG. 1, to accomplish this. By the time the first coil charged into the furnace reaches the unreeling station 29, nine of the ten turntables will carry such coils, that coil located at the unreeling station now being properly heated and ready for feeding into the forging apparatus 23. This latter step is accomplished by an operator, aided by mechanism to be described, grabbing an end of the coil with suitable tongs and feeding it to the known receiving mechanism of the forging apparatus 23. This forging apparatus will pull the hot coil of rod therethrough, forming grinding balls which are then transferred by turntable 26a and conveyor 26b to the grinding ball sizer 24 which will finish them and send them on their way to storage by means of the mechanical conveyor 25a and the gravity conveyor 25b. As soon as the first turntable to reach the unreeling station is relieved of its coiled rod in this manner, the hearth will be indexed to bring the next turntable into position for immediate feeding of its coiled rod to the forging apparatus 23 while an additional coil is placed on the previously empty turntable 30 when moved into position before the charger 27. This operation will continue in this manner so long as it is desired to manufacture finished grinding balls.

Referring now to FIGS. 2, 3, 4 and 12, certain of the features of the rotary hearth furnace 20 will be described in greater detail. As indicated in these figures, the walls 35, including also the ceiling and the rotary hearth or floor 36, are made of or lined with refractory material, as will be understood by those skilled in the art. With respect to the hearth 36, it includes a steel plate 37 attached to suitable frame members generally indicated at 38. As perhaps best seen in FIGS. 3 and 12, the frame structure 37-38 includes a first, annular outer rail 39 attached thereto and from which depends a second, annular outer rail 40 having a member 41 which engages a plurality of rollers 42 suitably supported in bearings 43 disposed on a building floor beneath the hearth 36. Similarly, there is a first annular inner rail 44 fixed to the frame structure 37-38 and a second annular, inner rail 45 depending from the rail 44 and having a member 46 resting on a plurality of rollers 47 suitably supported in bearings 48 placed about the building floor beneath the hearth. In this manner the reinforced hearth 36 is supported on the plurality of rollers 42 and 47.

FIG. 4 diagrammatically represents more detail respecting the location of the rollers and bearings 42, 43 and 47, 48. These support rollers or wheels 42 are designed to be engaged by the rail members or outer tracks 39-41 while the support rollers or wheels 47 are designed to be engaged by the inner rail or track members 44-46. Also spaced about the underside of the hearth frame structure are a plurality of track stabilizing wheels 49 and 50 for the outer and inner tracks respectively. The unreeling pit, in which the lifting mechanism, to be described, is located is shown at 29a in FIG. 4, and the charging pit for housing its lifting mechanism, to be described, is indicated at 280. A plurality of frame members 51 are diagrammatically shown in FIG. 4 as constituting a part of the understructure supporting the plate 37 and hearth 36. The indexing means, to be described in detail in connection with the description of FIG. 5, is generally indicated at 52 in FIG. 4. A circular indexing rail will be fastened to the underside of the hearth frame structure, as will be described in connection with FIG. 5.

Referring now to FIGS. 2 and 3, other features of the rotary hearth construction will be described. The right hand side of FIG. 3 depicts a portion of the charging station 28 while the left hand side of FIG. 3 depicts a portion of the unreeling station 29. The lift mechanisms for both stations have been omitted; these are shown, and will be described later, in FIGS. 9 through 11 and 6 through 8 respectively. The turntables 30 normally rest on the frame structure 3743, 44-48 and various of the web members 51. Openings 53, therefore, are provided in the hearth 36 and these openings are of greater diameter than those of the turntables 30. This insures that, even in the down position wherein the turntable is resting on the frame structure, the turntables 30 will not be in direct contact with the hearth 36. This prevents damage to the hearth and to the turntables which might otherwise occur should the refractory materials of which end is made come into contact with one another. The turntable 30 at the charging station 28, as shown in FIG. 3, is in its normal, down position wherein it is resting on the frame structure while the turntable 30 at the unreeling station 29 is shown, in FIG. 3, in its unreeling position wherein it has been lifted, by mechanism to be described but not shown in FIG. 3, off the frame structure.

Referring now to FIG. 5, the indexing mechanism for rotating the hearth 36 will be described. This mechanism 52 includes brace structure 54 mounted on the building floor. Connected to the structure 54 is a piston-cylinder arrangement 55. Pivotally connected to the piston-cylinder arrangement 55, as indicated at 56, is a carriage 57 having a spring biased dog 58 mounted thereon. The dog 58 is normally biased to the position shown in FIG. 5. An indexing rail 59 having flanges 60 is suitably secured to the frame understructure generally indicated at 38a. The carriage 57 is supported from this indexing rail 59 by pairs of rollers 61 and 62 which ride on the flanges 60 on either side of the rail 59. These rollers 61 and rollers 62 are mounted on bracket members 63 and 64, respectively, connected to the carriage 57. The underside of the rail is provided with a series of dogs 65 spaced completely around the hearth. The dogs 65 are arranged to be engaged by the carriage dog 58.

Upon actuation of the piston-cylinder arrangement 55, by control means not shown, but in such manner as will be readily understood to those skilled in the art, the carriage 57 advances and the dog 58 engages a dog 65 whereby the frame structure and hearth will be moved the length of the piston stroke. When the piston is retracted, the dog 58, being spring biased, will pass beneath the next dog 65 to the rear of that initially engaged whereupon further actuation of the piston will result in the dog 58 engaging such next dog 65 to again advance the hearth. Depending on the size of the furnace, the number of turntables and similar dimensions of the piston cylinder and spacing of the various dogs, one or more actuations of the piston-cylinder 55 may be required to index the hearth so as to move the various turntables from one position to the next.

Turning again to FIG. 12, mechanical means are illustrated for sealing the rotary hearth furnace. As shown, an L-shaped bracket 66 is secured to the frame structure 38. A similar L-shaped bracket 67 having an upturned portion 68 is secured to the stationary furnace wall 35 as indicated at 69. A J-shaped member 70 has a downwardly turned portion 711 which hooks over the upturned portion 68 of the member 67. As the hearth 36 is indexed within the confines of the stationary furnace wall 35 by the mechanism described in connection with FIG. 5 and generally indicated in FIG. 4, the member 66 will slide along the members 70 whose hinging action from fulcrums at 618 permits movement to allow for heat expansion and the escape of debris, especially scale. Also of importance is that the furnace is sealed from undue loss of heat.

FIGS. 6, 7 and 8 disclose lift mechanism generally indicated at 72 for the turntable 30 when located at the unreeling station 29.

This mechanism includes a supporting platform 73 having an upstanding nose 74- located centrally thereof. This nose is designed to register within a corresponding opening located in the center of the lower part of each of the turntables 30, such an opening being indicated at 75 in the left hand side of FIG. 3. The platform 73 rests on bearings 76 located on a member 77 which is supported from a first table member 78 by a plurality of braces 79. Suitably supported from the first table member 78 is a reversible motor 80 the output end of which is connected by a belt or chain and sprockets 81 to suitable pulley mechanism 82. This mechanism drives, by conventional means not shown but generally located within the housing 83, a shaft 84 connected to the platform 73. Actuation of the motor 80 may rotate the platform 73 in either direction as desired.

The mechanism 72 includes a first set of cylinders 85 having pistons 86 movable therein by conventional means, as will be understood by those skilled in the art. A second table member 87 is secured to the ends of the pistons 86. A second set of cylinders 85a is secured to the bottom of the table member 87 and is provided with piston 88 which are connected to the first table member 78.

The platform 73 and associated mechanism is shown in its retracted position in FIG. 6 at which time it will be understood that the mechanism 73-74 is beneath and out of the way of the frame structure connected to the underside of the hearth 36. The lift mechanism 72 is designed to permit upward movement of the platform 73 by successive increments to two positions. When the pistons 86 are actuated, the tables 78 and 87 are moved to a first position wherein the platform passes upwardly through the hearth frame structure, through the opening 53 of the hearth floor 36 and into contact with the underside structure of that turntable 30 then located within the unreeling station 29 so as to move the turntable off of the hearth frame structure a short distance. The turntable 30 and coil 32 (see FIG. 2) of rod material will then be supported solely by the platform 73 and the related mechanism generally indicated at 72. At this first position it is possible to rotate the platform 73 in either direction by actuation of the reversible motor 80. This will enable an operator to so position the coil 32 that he can grab the end thereof by a pair of tongs inserted through a small door so as to pull the end out of the furnace and into the forging apparatus 23. After the end of the rod 32 is engaged within the forging apparatus 23, clutch mechanism, not shown, for the motor mechanism 80-84 may be released whereafter such turntable power means 80-84 may be used as a slight drag on the coil to create a small amount of desired back tension as the coil is fed into the forging apparatus. The position of the tables 78 and 87 after upward extension of the pistons 86 is illustrated in FIG. 7. At this point the nose 74 has engaged within the opening 75 and the turntable 30 is supported on platform 73.

At times it may be necessary to clear debris which may collect between a turntable 30 and the hearth. This can be accomplished by the upward extension of pistons 88 which raise plate 78 above plate 87. Raising plate 78 results in the lifting of support platform 73 and a turntable30 to a higher position. This higher, up position can be reached only after an initial up position is established by pistons 86 as indicated in FIG. 7. Any debris collecting within the furnace may be removed therefrom via the now more greatly exposed opening 53. This is the condition illustrated in FIG. 8. When it is time to index another coil of rod into position to be unreeled into the forging apparatus, the platform 73 and related mechanism are first returned to the retracted position of FIG. 6 wherein it will be out of the way of the frame structure connected to the bottom of the hearth 36. The hearth is then indexed into such position that another coil of rod is placed within the unreeling station and another, now empty, turntable is positioned within the charging station.

The lift mechanism for the charging station 28 is generally indicated at 90 in FIGS. 9, l and 11. This mechanism includes a support platform 91 having a centering nose 92 designed to engage within the opening 75 provided in the bottom of the turntable 30 and related structure. The mechanism 90 includes a first set of cylinders 93 having pistons 94 and a second set of cylinders 95 having pistons 96. The second set of cylinders 95 is connected to frame structure 97 which is in turn connected to the ends of the pistons 94.

The lift mechanism 90 is shown in FIG. 9 in its retracted position at which time the platform 91 and centering means 92 are beneath and out of the way of the frame structure supporting the hearth. When a coil of rod is to be charged onto a turntable located at the charging station 28, the pistons 94 are actuated so as to bring the platform 91 to the position indicated in FIG. 10. In this figure it will be understood that the platform 91 has engaged the bottom of a turntable 30 and has lifted the turntable from its original position of support on the hearth frame structure. The first position shown in FIG. is to stabilize the turntable and to relieve the hearth frame structure from the shock that occurs when a coil of rod is deposited on a turntable.

Sometimes it becomes necessary to remove a turntable from the furnace so as to repair it or replace it with another turntable. By raising the turntable above the position shown in FIG. 10, the same mechanism which deposits a coil on the turntable may be used to engage beneath the turntable and thereby remove it from the furnace; this is the position in FIG. 11. Thus when the pistons 96 are actuated, the support platform 91 is moved further upwardly so that the charger 27 may be actuated to withdraw the turntable 30 from the furnace. The mechanism is returned to the retracted position of FIG. 9 before the hearth 36 is indexed again.

The construction of a turntable 30 is similar to that of the hearth 36 in that there may be a bottom plate 98 secured beneath the refractory material and above the rail-frame supports 99, see FIG. 3. Also, it will be obvious that the lift mechanisms 72 and of FIGS. 6 through 8 and 9 through 11, respectively, will be positioned at the unreeling and charging stations 29 and 28, respectively, as generally indicated in FIG. 2.

It is believed that the foregoing constitutes a complete description of the rotary hearth furnace and the system for forming balls of which it is a part. It will be apparent to those skilled in the art, however, that modifications may be made in the furnace and system without departing from the scope and spirit of the invention as set forth herein. 1

Although the furnace and system have been described with reference to particular structures and arrangements, such structures and arrangements are not to constitute a limitation on the invention as claimed except insofar as such structures and arrangements are specifically set forth in the subjoined claims.

In a typical rotary hearth furnace constructed according to this invention ten combination spindleturntables may be spaced around the main rotary hearth. This hearth, for example, may have a diameter of 27 feet with the spaced turntables each having a diameter of five feet. Each turntable may hold up to 2500 lbs of coil. The total weight on a single turntable does not have to be all in one coil; two 900 lb. coils, for example, could be placed on each turntable. In the case of two-coil feeding, the operation would begin with a first turntable in the rotary hearth being indexed to the unreeling station for feeding the forging apparatus. The first coil would be fed into the forging apparatus and the second coil immediately afterwards. The hearth is then promptly indexed again and the operation repeated. New coils may be loaded an an empty turntable at the loading station while a feeding operation takes place.

In the operation above described, continuous production is dependent upon having sufficient capacity for heating a particular rod size. It is believed that changes in furnace dimension or burner size, which could adjust the heating capacity to adapt to a different rod size, do not alter the scope and/or spirit of this invention. In any case, the furnace of this invention makes possible a rate of feeding the forging apparatus and, therefore, the production of grinding balls, at high speeds not previously obtainable.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A system for forming balls which comprises: a loader for loading cold coils of rod of desired material; a coil conveyor to receive coils from said loader; a charger to receive coils from said coil conveyor; a furnace into which said charger deposits said coils and having a single, unitary heating chamber and a horizontally disposed rotary hearth therefor, said hearth having a plurality of vertical openings therein, each opening have a horizontal turntable therein to receive at least one of said coils, frame work supporting said hearth and on which said turntables rest, said furnace having a charging station and an unreeling station, and means to index said hearth so as to bring a said turntable from said charging station to said unreeling station; a ball forming apparatus for forming balls from rod and located so as to receive hot rod directly from said furnace; and a sizer for finishing said balls and located so as to receive said balls directly from said ball forming apparatus; whereby said ball forming apparatus may be 3. The system of claim 1 in which said furnace is provided with a second lift mechanism for said unreeling station, said second mechanism having motor means to rotate a said turntable engaged thereby, whereby said second mechanism may lift a turntable from said frame work whereafter said turntable may be rotated by said motor means. 

1. A system for forming balls which comprises: a loader for loading cold coils of rod of desired material; a coil conveyor to receive coils from said loader; a charger to receive coils from said coil conveyor; a furnace into which said charger deposits said coils and having a single, unitary heating chamber and a horizontally disposed rotary hearth therefor, said hearth having a plurality of vertical openings therein, each opening have a horizontal turntable therein to receive at least one of said coils, frame work supporting said hearth and on which said turntables rest, said furnace having a charging station and an unreeling station, and means to index said hearth so as to bring a said turntable from said charging station to said unreeling station; a ball forming apparatus for forming balls from rod and located so as to receive hot rod directly from said furnace; and a sizer for finishing said balls and located so as to receive said balls directly from said ball forming apparatus; whereby said ball forming apparatus may be substantially continuously fed with hot rod from said furnace so as to produce said balls at an extremely fast rate.
 2. The system of claim 1 in which said furnace is provided with a first lift mechanism for said charging station whereby said mechanism may lift a turntable from said frame work before a said coil is deposited thereon by said charger.
 3. The system of claim 1 in which said furnace is provided with a second lift mechanism for said unreeling station, said second mechanism having motor means to rotate a said turntable engaged thereby, whereby said second mechanism may lift a turntable from said frame work whereafter said turntable may be rotated by said motor means. 